There are 4 purposes of this study: (1) to compare the efficacy of continuing AZT/ddI vs adding 3TC or switching to AZT/3TC. (2) to determine the influence of virus load, CD4+ cell counts, biologic phenotypes and the presence of symptomatic HIV disease on the response to a new therapeutic regimen. (3) to determine the influence of virus load, CD4+, and biologic phenotypes and the presence of symptomatic HIV disease on the kinetics of viral replication. (4) to determine the influence of virus load, CD4, biologic phenotypes, and the presence of symptomatic HIV disease on the rate of emergence of the 3TC associated resistance mutation at codon 184.